Floating roof



R. C. ULM

FLOATING ROOF Feb. 16, 1954 Filed June 23, 1950 FIG. 3

INVENTOR.

6 Z/hz D. W

Patented Feb. 16, 1954 UNITED STATES PATENT OFFICE FLOATING ROOF Reign. Ulm, East Chicago, Ind., assignor to Graver Tank & Mfg. 00., Inc., East Chicago, Ind.,,a corporation of Delaware.

Application June 23, 1950, Serial No. 169,871

Claims. 11

This invention relates to floating roofs as used in liquid storage tanks. It has particular reference to flexible, centrallyweighted, single deck floating roofs of the liquid contacting type, mainly when the tanks and roofs are very large, having diameters in excess of about 100 or 120 feet.

Flexible, centrally weightedfloating roofs of the liquid-contacting type have a deck which, in vertical cross-section, has a contour curve rising from the weighted center to a peripheral upstanding rim, due to the interaction of the various forces acting upon the deck. This contour curve isrelatively steep in the central parts and relatively flat in the outer parts of the deck, thereby creating a problem of rain water drainage and gas or vaporremoval, in said outer parts. This problem is most pronounced in large floating roofs of this type, that is, in floating roe-is with a diameter greater than about 100 or 120 feet. In floating roofs of such a size the required inward-downward slope, for instance a pitch of about 1:50 in the outer parts, tends to produce a contour curve with rather excesive pitch in the central'parts. This inturn leads to very deep immersion of the central weight, to high central forces of buoyancy, to the needfor a very heavy central weight, to the imposition of very high stresses upon the flexible deck, and thus to a relatively expensive construction. This follows from known facts about said contour curve as disclosed Patent No. 2.491047 grantedto F111 Prager and myself on February '7', 1950, and in my further applications filed October 21, 1949, and February 23, 1950, under Ser. Nos. 122,639 and 146,503, now issued as Patents 2,531,897 and 2,531,898.

My present application covers a further improvement, using a shape as previously disclosed and providing a special means to maintain such shape. It also reduces the total weight and cost of the floating roof. The shape is maintained against forces which tend todestroy it. The total weight and cost are reduced by means of a further development, utilizing the shape-maintaining members for the required reenforcement of the rim around the deck.

Tendencies to destroy the required shape, and to form an outward-downward slope in peripheral parts of the roof, are due to the inherent weight of theperipheral rim reinforced against loads due'to. the central ballast, andthe additional weight of seal and other mechanisms supported bythe rim or by the peripheral part of, the deck. In order to counteract such tendencies it is desir- 2 able, mainly in large floating roofs of this type, to provide forces of buoyancy in the peripheral parts, compensating for the extra weight of those parts.

In certain roofs known to the art a plain, annular, peripheral pontoon has been used, for other purposes. The use of such a pontoon would have undesirable side effects in the present case since it would interfere with the removal of gases and vapors. Therefore I apply the required force of buoyancy by a discontinuous series of peripherally located buoyant members, generally provided by spaced, hollow boxes below the deck. It has further occurred to me that such boxes can be tied together to form a novel reenforcement for the rim. Thus the buoyant members both compensate and reduce the extra weight.

In the drawing Fig. 1 is a diagrammatic crosssectional elevation of apparatus constructed in accordance herewith. Fig. 2 is an enlarged detail from Fig. 1. Fig. 3 is a section through Fig. 2 along lines 3-3. Fig. 4 shows a modified construction in a view generally similar to Fig. 3.

The floating roof R rests on the surface S of the liquid product L stored in the tank T. The roof R rises-and falls with the liquid surface S, as liquid is introduced or withdrawn through piping P. The roof R is slightly smaller than the tank T,thereby leaving an annular space A between the roof and the inside of the tank T. A peripheral, annular seal mechanism diagrammatically represented by letter M bridges the annular space A. This mechanism is sufiiciently elastic to adapt itself to local irregularities of the annular space, while being sufficiently sturdy to withstand the friction imposed by frequent rising and falling movements of the floating roof.

The seal mechanism M is supported by and directly from the rim plate ii at the periphery of the floating roof R, which plate is upstanding and usually cylindrical. This rim plate [0 one of the basic parts of the floating roof R, as is the single deck ll lying on the liquid surface S and secured to the rim plate iii below the upper edge of the latter. A pan iii-4 i is formed in this manner, which pan is capable of floating on the liquid surface S even when the liquid L is light, like water or gasoline, and the material for the floating roof R. is heavy, like steel plate or the like. An additional important part of the flexible floating roof R is the central ballast weight l2, which is heavy enough to keep the entire deck I I inwardly and downwardly inclined in substantial accordance with the contour curve as mentioned, thereby assuring practically complete removal of vapor and gas to the annular space A, and of rain water to the drain 13; said drain connecting a central part of the space above the deck with a lower space outside the tank, in manner well known to the art.

When the tank is drained of liquid product for maintenance purposes the floating roof R rests on feet or support members F, which are desirably mounted on the deck ll so that they can be vertically adjusted from the top of the deck in well known manner. In a centrally weighted floating roof most if not all of these feet F are installed in and distributed along the peripheral part of the deck, it being undesirable to subject the body of the deck to concentrated weight loads due to such feet, which would tend to form rain water retaining and corrosion inducing pockets in the deck. Being substantially limited to the peripheral part of the roof, the series of supporting feet constitutes." an addition to the inherent'weight of the peripheral part itself.

Some additional support feet F are desirably installed in locations adjacent to and surrounding the central ballast weight l2, in order to relieve the outer feet F of the high extra loads that would otherwise be imposed; it being desirable to suspend the ballast weight as well as the deck above the bottom of the drained tank, in order to allow maintenance operations on the underside. Accordingly, when the tank is drained, the feet F and F support the roof; when the tank is in use the floating roof supports the feet and is in turn supported by the liquid product.

For the basic purpose of covering th liquid surface S it has long been known to be necessary and sufficient to form a deck it from steel plates about or thick, which weighs about 8 or 10 lbs. per sq. ft. A pan iii-li formed of & steel and not centrally or peripherally weighted would tend to float about 1.5% or 1.74 below the liquid surface S, depending on whether the liquid is water or gasoline. The provision of the central ballast weight !2, which is necessary to insure central drainage etc. increases the basic weight of the floating roof, usually by about to 36%, and tends to produce said contour curve, as a result of which the center of the deck float several inches deeper, and the avegage immersion of th roof is about 2 to 2.25".

The upstanding and generally reenforced rim ii), the seal mechanism M and the peripheral feet F add weight to the peripheral parts of the roof. As a result there is a tendency for a reversal of the contour curve, that is, for the development of such a curve which runs outwarddcwnward, instead of outward-upward, adjacent the rim Ii This tendency, which is objectionable since it interferes with simple methods of drainage and gas removal, is particularly outspoken in large roofs R.

The addition of weight due to the rim plate Hi and its required reenforcements depends largely on the size of the roof. In roofs of 100 to 160 ft. diameter this item usually adds 12 to 18 lbs. per linear foot of roof periphery; the heavier rim being required for the larger roofs. The sealmechanism M adds about to 35 lbs. per linear foot; the heavier mechanisms being required when the tank is riveted, and lighter ones when it is welded. The feet F usually add about 10 lbs. per linear foot. Accordingl the peripheral parts of a large roof added to the deck have a total weight of 47 to 63 lbs. per foot of roof periphery.

It can be assumed that most of this extra weight is supported by the reenforced, peripheral, annular area of a floating roof of the type in question, which area is about 2 to 6 feet wide, depending on the diameter of the roof. It can be assumed that substantially all of this extra weight is supported by such reenforced area plus an annular area directly inside therefrom, which is about 1 foot wide. Thus the extra weight is distributed over a ring of 3 to '7 feet width, and constitutes a downward load of about 9 to 16 lbs. per sq. ft., or more usually, as I find in practice, about 11 to 14 lbs. per sq. ft. over and above the weight of the ring-shaped deck portion itself.

I install peripheral, hollow, buoyant box members B to compensate this extra weight load of ll to 14 lbs. per sq. ft. More specifically I install a discontinuous series or plurality of separate buoyant members B, spaced along and below the peripheral part of the deck ll, with open spaces between these box members, in order to allow peripheral removal of gas or vapor.

Theoretically I could make these box members B in any one of several forms. Particularly their radial extension below the roof could be made greater or less great, so long as they un-' derlie the said ring of 3 to '7 feet width. Prac: tically I found it most desirable to make these box members rather flat and to give them a radial extension at least as great or sometimes greater than said ring; making them large enough to displace, when immersed slightly beyond the peripheral edge of deck l l as shown, an amount of liquid L substantially balancing the weight of the box members B themselves plus said peripheral extra weight. Only exceptionally is it desirable to provide, additionally, pontoon means to displace an amount of liquid balancing, a temporary extra weight of rain water which may accumulate largely in central regions of the roof due to insufficient drainage facilities I3. For this added function I prefer to provide pontoon means elsewhere than in the peripheral zone; for instance to make the ring-shaped area occupied by the box members B about one-third to one-half of the total roof area, using the onehalf proportion in the smaller roofs considered herein and the one-third proportion in larger ones. On the other hand this extra protection against rain can be dispensed with, in certain cases. ,The aforementioned load-supporting ring of 3 to '7 ft. width used in this event represents only about one quarter to one fifth of the roof area; and the area of the ring of box members can well be even somewhat smaller.

I secure these box members B rigidly to the underside of the deck H and the inside of the rim H), which rim for this purpose is extended downwards below the deck. Thus the box members B are partially formed by the outer parts I4 of the deck and thelower part [5 of the rim plate. They are completed by inner walls [6 more or less parallel with the rim plate; together with bottom walls Hand endwalls it running more or less radially of the roof. y

I interconnect the inner or bottom walls H or IE of adjacent boxes-B by bottom tie plates or structures I9, spaced below the deck II and spaced inwardly of the rim plate Hi. In the embodiment as shown in Fig. 2, tie plates I9 effectively interconnect both sets of members 16 or H, the tie plates being secured to the joints between these members. In this manner the series of boxes B is tied together into a rigid ring, thereby dispensing with the need for the rigid ring of reenforcements for the: rimplate, here,- tofore used in floating roofs of this. type. This in turn provides a further improvement of the drainage of rain water from the peripheral areas of the roof. At the same time the removal of vapor and gas from underneath the roof remains feasible, being allowed by suitable slots or apertures 20 in the lower part l of the rim plate 10, directly below the deck I! and between pairs of boxes B.

In a number of instances it is desirable to install additional hollow boxes above the deck H, in the peripheralpart of the roof. Such an upper box 2! is shown in Fig; 4; Desirably it is formed in part by the rim plate and deck and in other part by a top plate 22 extending inward-downward from the rim plate ID with a greater inclination than that of the outer parts of the contour curve, in order to safeguard more positive drainage of rain water from the large outer areas of the roof.

Such an upper box 2! will also prevent the rain water temporarily collected on the roof from excessively shifting the center of gravity due to wind action and the like, since it will collect the total amount of water retained in a relatively small annular area between the center weight i2 and the upper box 22.

Of course an upper box of this type adds to the total weight of the roof while not contributing to its buoyancy. It also adds to the rigidity of the peripheral part of the roof, thereby allowing the use of lighter and more economical members it, It, l1 and I9.

It will be obvious to persons skilled in the art that a number of further modifications are possible. I claim:

1. A floating roof for a liquid storage tank, comprising a single deck; a rim surrounding an annular, peripheral part of the deck and extending above and below the same; drain means connecting central parts of the space above the deck. with a lower space outside the tank; vent means connecting outer parts of the space below the deck with a space unconfined by the deck; ballast weight means secured to and supported by a central part of the deck and heavy enough to maintain a contour curve, in any vertical cross-section of the deck, upon immersion of the deck in the stored liquid, which curve rises relatively steeply from the central part of the deck connected to the ballast weight while being relatively flat in outer parts of the deck; and a pontoon ring formed in part by a lower portion of the rim, said pontoon ring being located at least in part below the peripheral part of the deck, being secured to said peripheral part, and displacing, when immersed slightly beyond the elevation of said peripheral part, an amount of stored liquid which substantially balances the weight of the rim and pontoon ring plus that of any equipment secured to the rim and pontoon ring; whereby upon immersion of the floating roof in the stored liquid no outward-downward slope is formed even in the outer and peripheral parts of the deck, while the ballast weight means and the entire floating roof can be relatively light.

A floating roof for a liquid storage tank, comprising a single deck; a rim secured to the periphery of the deck and extending above and below the same; drain means connecting central parts of the space above the deck with a lower space outside the tank; ballast weight means secured to and supported by a central part of the'deck and heavy enough to-maintainw an out..- wardly rising contour curve: in any vertical crosssection of the deck, upon immersion of the. deck in the stored liquid, at least the topv of the deck being entirely unobstructed from the ballast weight means to the periphery of the deck'and floating roof; and. a ring or pontoons below the deck, the pontoons being separated by open vent spaces and: the ring being formed in part by a lower portion of the rim and. in. part by. tie members spanning. the open vent spaces, whereby reenforcement. of the rim against loads dueto the ballast weight means. need not be effected by reenforcement members secured to the top of the deck and obstructing the same, the lower part of the rim being apertured at the end of each vent space, and the ring of pontoons displacing, when immersed slightly beyond the elevation of said peripheral part, an amount of the stored liquid which substantially balances the weight of the rim and pontoon ring plus equipment secured thereto.

3. A floating roof for a liquid storage tank, comprising a single deck; a rim surrounding an annular, peripheral part of the deck and extending above and below the same; drain means connecting central parts of the space above the deck with a lower space outside the tank; vent means connecting outer parts of the space below the deck with a space unconfined by the deck; ballast weight means secured to and supported by a central part of the deck and heavy enough to maintain a contour curve in any vertical cross-section of the deck, upon immersion of the deck in the stored liquid, which curve rises relatively steeply from the central part of the deck connected to the ballast weight while being rela tively flat in outer parts of the deck; and a pontoon ring formed in part by a lower portion of the rim, said pontoon ring comprising hollow chambers above and below the peripheral part of the deck, being secured to said peripheral part, being large enough above the deck to confine any rain water falling on the roof within a relatively small, inner space, and displacing, when immersed slightly beyond the elevation of said peripheral part, an amount of the stored liquid which substantially balances the weight of the rim and pontoon ring plus that of any equipment installed on the rim and pontoon ring.

4. A floating roof for a liquid storage tank comprising a single deck; a drain means connecting central parts of the space above the deck with a lower space outside the tank; vent means connecting outer parts of the space below the deck with a space unconfined by the deck; ballast Weight means secured to and supported by a central part of the deck and heavy enough to maintain a contour curve in vertical cross sections of the deck upon immersion of the deck in the stored liquid which curve rises relatively steeply from said central part of the deck while being relatively flat in outer parts of the deck; and a hollow rim secured to an annular, peripheral part of the deck, extending above and below the same and displacing when immersed in the stored liquid to an elevation between said peripheral part and the top of the hollow rim, a volume of the stored liquid the weight of which substantially equals that of the hollow rim plus any equipment installed thereon.

5. A floating roof for a liquid storage tank comprising a single deck; a drain means connecting central parts of the space above the 7 deck with a. lower space; vent means connecting outer parts of the space below the deck with a space unconfined by the deck; ballast weight means secured to and supported by a central part of the deck and heavy enough to maintain a contour curve in vertical cross sections of the deck upon immersion of the deck in the stored liquid which curve rises relatively steeply from said central part of the deck while being relatively flat in outer parts of the deck; and a hol 10w pontoon ring structure secured to an annular, peripheral part of the deck and extending above and below the same in order to support its own weight and that of any equipment installed thereon.

. REIGN C. ULM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,463,268 Huff July 31, 1923 2,071,530 Howard Feb. 23, 1937 2,089,645 Dickmann Aug. 10, 1937 2,359,416 -Hammeren Oct. 3, 1944 2,386,022 Wiggins Oct. 2, 1945 2,497,047 Prager Feb. 7, 1950 

